heightmap insertion unsuccessful with gazebo 7

I want to use heightmap created by myself in gazebo, and I`ve followed tutorials like this one and this. I use Ubuntu 16.04 and gazebo 7 as the second tutorial requires.

At first , I created a heightmap as the first tutorial instructed, and I tested with my gazebo. It worked out, though occasionally the heightmap wasn't loaded fully . Only half of the terrain was loaded, and the other half was flat.

But after a few hours I tried again. But no matter how I try , my gazebo always crashes after I insert heightmap.
And the error msg is always the same:

I've checked a question asked by others before.But is there any better solution to this problem?
Updating gazebo to 8 may work, but it's not convenient and the tutorials insert heightmap with gazebo 7 successfully.